Link users to Issues imported from Phabricator

For each user mentioned in the task JSON, we should find all the related users, for that we'll need the user.search API call, and we should pass it all related user phids as constraints:

{ "phids": [ "PHID-USER-hi", "PHID-USER-ha" ]}

The user's we'd need to link can be found in these fields:

subscribers => GitLab subscribers.

authorPHID => Issue Author

ownerPHID => Assignee

We should try to find this phid in a redis cache first, mapped to a GitLab user ID, if it does not exist we'll make the API call to Phabricator, to find the username for the user. Then, if a user with the same username exists on the GitLab instance, we use that, otherwise, we'll use the Ghost user.

When looking for users by username we should limit to users that have access to the project.